The present invention relates to antisettling compositions in liquid pourable form that provide excellent pigment suspension and rheological properties to aqueous coating compositions.
It is known in the art to add pigment suspension or antisettling agents to coating compositions to prevent pigments or other finely divided solid particles from settling during storage. Depending on the hardness of the settling, it is difficult, and sometimes not possible, to evenly redisperse by stirring the solid material throughout the coating system. The art has constantly sought materials that are useful to control the rheological properties and pigment suspension properties of aqueous fluid systems containing finely divided solid particles and, additionally, are easy to use.
One type of material which has been shown to be useful as antisettling or pigment suspension agents for organic (or non-aqueous) coating compositions are emulsifiable polyethylene waxes dispersed in organic solvents as disclosed in U.S. Pat. Nos. 3,123,488 and 3,184,233. Additionally, U.S. Pat. No. 3,985,568 discloses a creamy paste comprising finely divided particles of an emulsifiable polyethylene wax suspended in a sulfated/sulfonated castor oil solution which is useful for modifying the rheological and suspension properties of non-aqueous fluid systems containing finely divided solid particles. Moreover, U.S. Pat. No. 4,975,119 discloses a liquid antisettling composition for organic coating compositions which comprises at least one emulsifiable polyethylene wax, at least one salt of an alkyl hydrogen sulfate, at least one salt of a reaction product of a polyvalent inorganic acid and a fatty ester compound or fatty acid derivative, an organic solvent and, optionally, water.
U.S. Pat. No. 3,937,678 discloses a process for improving the rheological properties and suspension properties of non-aqueous fluid systems containing finely divided solid particles by adding to the non-aqueous fluid system a mixture of an amide wax having a melting point of from about 100.degree. C. to about 160.degree. C. obtained by reacting hydrogenated castor oil fatty acid or an organic mixture containing at least 30 molar percent of hydrogenated castor oil fatty acid with amines, and an emulsifiable polyethylene wax having an acid number of from about 2 to about 50, a softening point of from about 95.degree. C. to about 120.degree. C., a density of from about 0.92 to about 0.98, and a penetration hardness of from about 1 to about 20.
Emulsifiable polyethylene waxes find, however, limited use as pigment suspension or antisettling agents in aqueous or water-borne coatings systems. Japan Kokai 76 04 087 discloses the use of emulsifiable polyethylene waxes to stabilize a dispersion of pigments in water thinned coating compositions where the emulsifiable wax is dispersed in xylene solvent which results in a paste and the thinner is a butyl cellosolve/isopropyl alcohol/water solvent system.
Typically, thickeners such as fumed silica or clays such as montmorillonite, hectorite, or attapulgite have been used in aqueous coating systems to correct pigment settling problems. However, these materials have the disadvantage of lowering the gloss associated with the cured coating system and are difficult to use as a post-add correction at the completion of the preparation of a paint. These materials are difficult to disperse during the manufacture of paints and require high shear mixing equipment to achieve adequate dispersion.
Other thickeners which act as stabilizing agents to deter sedimentation include the natural gums, for example, xanthan gum, alginate, gum arabic, guar gum, tragacanth gum, and locust bean gum; cellulose derivatives such as carboxymethyl cellulose and hydroxyethyl cellulose, and modified starches.
Furthermore, the use of polyacrylic/acrylate thickeners such as CPE-15, WS-24, and Rheoplex B-505 commercially available from the Rohm and Haas Company have been reported in U.S. Pat. No. 4,432,797 as providing resistance to pigment settling in a water-borne wood stain. Additionally, pigment wetting agents or surfactants based on ethoxylated nonylphenols have been added to water reducible coatings for pigment suspension.
U.S. Pat. No. 4,071,487 discloses antisettling agents for use in pigmented aqueous lacquer systems wherein the agents are water dispersible (including water-soluble) amine salts of the products formed by reacting at 200.degree. C. to 250.degree. C., a C.sub.14-20 unsaturated fatty alcohol with an ethylene dicarboxylic acid to form a substantially neutral ester which is further reacted with about 1/7 to 1/35 of its weight with an ethylene dicarboxylic acid or anhydride compound. The amine neutralization is performed in organic solvents miscible with water which are stable on storage and may be incorporated into the lacquer at any point in its manufacture.
U.S. Pat. No. 4,439,575 discloses aqueous varnishes which contain mineral fillers and/or pigments and show virtually no sedimentation of the solid constituents. These varnishes are prepared by allowing a hot wax emulsion in water at between 80.degree. C. and 100.degree. C. to flow with vigorous stirring into the aqueous varnish containing the mineral fillers and/or pigments. Suitable waxes have a melting point above 60.degree. C. and a cloud point in toluene between 35.degree. C. and 45.degree. C. Particularly suitable waxes are montan waxes, which have been bleached and modified, or ester waxes based on modified montan waxes. The waxes can also be coupled with a nonionic emulsifier system.
In a field unrelated to antisettling additives, Japanese Tokyo Koho 81/09,522 discloses ethylene-maleic anhydride copolymers that are treated in the molten state with compounds having .gtoreq.20 H and/or primary or secondary amino groups to provide a modified ethylene-maleic anhydride copolymer with increased melt index, Young's modulus, and elongation.
Furthermore, U.S. Pat. No. 4,381,376 discloses a method for forming ionic copolymer salts from low molecular weight copolymer acids formed from ethylene and an alpha, beta-ethylenically unsaturated carboxylic acid having at least one carboxylic acid group, and cations having a valence of 1 to 3. In U.S. Pat. No. 4,603,172, the ionic copolymer salts of a low molecular weight copolymer acid of an alpha-olefin and alpha, beta-ethylenically unsaturated carboxylic acid are disclosed to be dispersion aids to disperse finely divided inert material such as pigments in a variety of non-acqueous polymer compositions including polypropylene and polyethylene. Allied-Signal, which owns said U.S. Pat. No. 4,381,376, sells AClyn ionomers which are low molecular weight ethylene-based copolymers neutralized with metal salts, including sodium, zinc, calcium and magnesium salts.
Other patents of interest include BASF U.S. Pat. Nos. 4,406,705 and 4,417,035 which relate to water emulsifiable hand waxes consisting of ethylene-carboxylic copolymers.
Accordingly, an ongoing search has been made for new additives for modifying the rheological and suspension properties of aqueous and water-borne fluid systems containing finely divided solid particles that are efficient, easily handled and readily dispersible in the aqueous fluid system requiring suspension properties.
The present invention overcomes the problems and disadvantages of the prior art by providing a homogeneous pourable liquid additive in water which provides excellent pigment suspension and rheological properties to aqueous coating compositions.
It is an object of the invention to provide a liquid, pourable composition that provides suspension properties to aqueous compositions containing finely divided solid particles, that is easy to handle, and is readily incorporated into aqueous compositions.
It is a further object of the invention to provide a liquid, pourable composition that provides suspension properties to aqueous compositions that are stable on storage and do not exhibit excessive syneresis.
An additional object of the invention is to provide a process for improving the rheological and suspension properties of aqueous compositions containing finely divided solid particles.
It is yet another object of the invention to provide stable suspensions of finely divided solid particles in aqueous compositions so that these particles do not exhibit excessive syneresis or hard settling during prolonged storage periods.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention will be realized and attained by means of the instrumentality and combinations, particularly pointed out in the appended claims.
To achieve the objects and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a liquid antisettling composition comprising (a) at least one low molecular weight copolymer of an alpha-olefin and an alpha, beta-ethylenically unsaturated carboxylic acid, (b) a neutralizing agent, and (c) water.
The liquid antisettling composition of the invention imparts suspension properties to aqueous compositions that contain finely divided solid particles and provides effective rheological properties to aqueous coating compositions. The liquid anti-settling composition of the present invention is highly efficient in suspension properties and can be used at lower loadings than commercially available products. The composition provides easier dispersion in aqueous paint systems than prior art pigment suspension or antisettling agents. Further, the composition of the invention can be incorporated in the coating composition at any stage of its manufacture which results in shorter processing time. Since the composition is in liquid form that is pourable and pumpable, it can be easily handled in a coatings manufacturing plant and thus reduces handling time and handling losses.
The invention also provides a process for improving the rheological and suspension properties of aqueous compositions containing finely divided solid particles comprising adding the liquid antisettling composition of the invention to an aqueous composition.
The invention further provides for aqueous compositions that contain the liquid antisettling composition that are stable suspensions of finely divided solid particles in aqueous compositions that do not exhibit excessive syneresis or hard settling during prolonged storage periods.